Ruby：如何在基类中调用派生类方法

Question

I want to Access the methods of the Derived class in the parent class. Please advice

Class A

 def methodA
 end

 def methodB
 end

end

Class B < Class A

 def methodC
 end

 def methodD
 end

end

I want to call methodD inside methodB

Class A
 def methodA
 end

 def methodB


 methodD
 end

end

Thanks.

Answer 1

What you wrote works, with some cleanups to the syntax. As long as your object is of the derived class B , then it knows what methodD is. In contrast, an object of class A will throw a NameError if you call methodB on it, since it doesn't know what methodD is.

class A

 def methodA
 end

 def methodB
   puts 'Called A#methodB'
   methodD
 end

end

class B < A

 def methodC
 end

 def methodD
   puts 'Called B#methodD'
 end

end

b = B.new
b.methodB
# Called A#methodB
# Called B#methodD

Answer 2

Just call the method.

class A
  def a
    b
  end
end

class B < A
  def b
    :b
  end
end

B.new.a
# => :b

Calling a method sends a message to the receiver, in this case the :b message. If the object responds to the message, then everything will just work.

You could also do this:

a = A.new

def a.b
  :x
end

a.b
# => :x

Answer 3

Take a look at the Template Method design pattern .

Class A
 def methodA
 end

 def methodB
 end

 def methodD
  raise NotImplementedError, 'Sorry, you have to override it!'
 end
end

Class B < Class A
 def methodC
 end

 def methodD
  puts "methodD"
 end
end

In this scenario, the methodD is called a Hook Method because basically inform all concrete classes that the method may require an override. The idea is: if the base implementation is undefined the subclasses must define the hook methods.